Solar control glazing

ABSTRACT

A heat treatable solar control glazing showing low-emissivity properties, and possibly also anti-solar properties, and methods to manufacture such a glazing. The glazing comprises a transparent substrate coated with a stack of thin layers comprising n functional layer(s) reflecting infrared radiation and n+1 dielectric layers, with n≥1, each functional layer being surrounded by dielectric layers. At least one dielectric layer above a functional layer comprises a layer consisting essentially of silicon oxide deposited by PECVD, and the stack comprises a barrier layer based on zinc oxide above and in direct contact with any functional layer which has a silicon oxide layer in the dielectric layer directly above it.

This application is a divisional of U.S. application Ser. No.14/894,420, filed Nov. 27, 2015, pending, which is a 371 application ofPCT/EP2014/061115 filed May 28, 2014, expired, and claims priority ofBelgium application number 2013/0384 filed May 30, 2013; Belgiumapplication 2013/0385, filed May 30, 2013, and Belgium application2013/0386 filed May 30, 2013 and claims benefit from EuropeanApplication 13197207.7 filed Dec. 13, 2013. The contents of each ofthese applications are incorporated herein by reference.

The present invention relates to solar control glazing showinglow-emissivity properties, and possibly also anti-solar properties,which can be incorporated into glazing for building or automotiveapplications.

Such glazing generally comprise a transparent substrate, e.g. a glasssheet, coated with a stack of thin layers comprising n functionallayer(s) based on a material reflecting the infrared radiation and n+1dielectric layers, with n≥1, each functional layer being surrounded bydielectric layers. The functional layer is generally a layer of silverof a few nanometres thickness, whilst the dielectric layers aretransparent and traditionally made of metallic oxides and/or nitrides.These various layers are commonly coated by vacuum coating techniques ofthe type magnetron sputtering.

Low-emissivity glazing have the property of reflecting infraredradiation for example emitted by the interior of building, therebylimiting heat losses. Often, at the same time, it is requested to have aluminous transmission (LT) as high as possible. These two requests, i.e.low emissivity and high transmission, generally lead to opposedsolutions in terms of structure. Therefore, it is necessary to makedifficult compromises. Glazing having solar protection properties allowsreducing the risk of excessive overheating due to sunshine, for exampleof a closed space having large vitreous surfaces, thereby reducing theair-conditioning requirements in summertime. In that case, the glazingshould transmit a total solar radiation energy as low as possible, i.e.have a solar factor (SF or g) as low as possible. It is however highlydesirable that a certain level of luminous transmission be guaranteed toensure a sufficient illumination of the interior of the building. Thesesomehow opposed requirements are reflected by the wish to obtain aglazing having a high selectivity (S), defined by the ration LT/SF.Having furthermore low emissivity properties, such glazing improve thethermal insulation of large glass surfaces and reduce energy losses andheating costs in cold periods.

Such glazing are generally assembled in multiple glazing units likedouble or triple glazing or laminated glazing, wherein the coated glasssheet is associated with one or more other glass sheet(s), coated ornot. The coating stack is positioned in contact with the space betweentwo sheets of glass, in the case of multiple glazing, or in contact withthe adhesive layer, in the case of laminated glazing.

In some case, it is necessary to mechanically reinforce the glazing by athermal treatment of the glass sheet to improve its resistance tomechanical constraints. It can also be necessary to bend the glass sheetat high temperature for specific applications. In the entire process ofmanufacturing glazing, it may be advantageous to heat treat glass sheetswhich are already coated rather than coating already heat-treated glasssheets. These operations are done at relatively high temperature, underwhich the functional layers reflecting the infrared radiation, forexample silver-based layers, tend to deteriorate and lose their opticalproperties and their properties vis-à-vis infrared radiation. Thesethermal treatments comprise heating the glass sheet to a temperature ofat least 560° C. in air, for example between 560° C. and 700° C., inparticular around 640° C. to 670° C., during around 3, 4, 6, 8, 10, 12or even 15 minutes according to the heat-treatment type and thethickness of the glass sheet. The treatment may comprise a rapid coolingstep after the heating step, to introduce stresses difference betweenthe surface and the core of the glass so that in case of impact, theso-called tempered glass sheet will break safely in small pieces. If thecooling step is less strong, the glass will then simply beheat-strengthened and in any case offer a better mechanical resistance.

In the case where the coated glass sheet necessitates a thermaltreatment, care must be taken to ensure that the coating stack canwithstand a heat-treatment of the type tempering or bending withoutlosing the optical and/or energetical properties for which it has beenmanufactured. Such stacks are sometimes called “heat-treatable” or“temperable”. Dielectric materials should be selected that do resist tohigh temperature without harmful structural modification: for example,zinc-tin mixed oxide, silicon nitride and aluminium nitride. Moreoverfunctional silver-based layers should not oxidise during heat-treatment,for example by ensuring that barrier layers are present which, duringthe treatment, oxidise themselves by capturing free oxygen or block suchoxygen migrating towards silver.

The coating stacks should simultaneously satisfy other conditions, likechemical and mechanical resistance and aesthetics (in particular coloursin reflection and transmission, the market generally requesting a colouras neutral as possible). The difficulty is to combine all theseconditions, optionally with the ability to undergo a heat treatment, tothe “basic” conditions of high luminous transmission, low emissivity,low solar factor. One additional difficulty comes from the manufacturingprocesses used to produce such glazing. The coating conditions, interalia the deposition speed, are dependent on the nature of the envisagedmaterials. For an economically acceptable industrial production, thespeed must be sufficient. It depends on multiple factors which guaranteethe process stability over the whole production time, on the wholesurface of the glass sheet and without defects in the coating.

Numerous solutions have been proposed to fulfil these variousrequirements, but no solution presently offers a glazing reallysatisfying at best all these requests.

EP803481 discloses heat-treatable low-emissivity single-silver anddouble-silver coating stacks of the type GL/D1/Ag/Ti/D2 andGL/D1/Ag/Ti/D2/Ag/Ti/D3 (where GL means glass and D means dielectric),wherein materials used in dielectrics comprise zinc-tin mixed oxide,zinc oxide and titanium oxide. Alternatively, EP1140721 describes heattreatable low-emissivity coating stacks of the type GL/D/Ag/AZO/D2(where AZO means aluminium-doped zinc oxide), wherein materials used indielectrics also comprise zinc-tin mixed oxide, zinc oxide and titaniumoxide.

However we have noted that stacks according to EP803481 suffered fromsome defects in terms of mechanical durability and that stacks accordingto EP1140721 showed haze and unacceptable spots after heat-treatment(see our comparative example 1 hereunder).

In our process of improving such traditional prior art coating stackswith a view towards the aim of our invention, we came acrossWO2007/080428 which already noted the same drawback of EP1140721 stacksand tried to solve it with a first dielectric comprising at least 3layers, in order from the glass substrate: aluminium (oxi)nitride/tinoxide or zinc-tin mixed oxide/zinc oxide, and a second dielectriccomprising at least two layers: a main zinc-tin mixed oxide layer and athin outermost protection layer of less than 10 nm thickness. However,we have noted that coating stacks according to WO2007/080428 also show anon-negligible drawback: their chemical durability before anyheat-treatment is not sufficient (see our comparative examples 2 and 3hereunder). However coating according to the present invention must beusable without subsequent heat treatment or stored before undergoing athermal treatment, therefore their resistance to ageing before heattreatment should be sufficient.

Furthermore the simple addition of a thin protective topcoat known toimprove mechanical durability to such traditional prior art coatingstacks has proven not to be sufficient to reach the level ofperformances aimed by the present invention.

EP506507 and WO2012/127162 both disclose single-silver infraredreflecting films ending with a SiO2 layer, respectively of around 25 nmand 40 to 120 nm. The stacks of EP506507 are said to be heat-treatable,whilst WO2012/127162 does not mention such feature. Both documentsdescribe a barrier layer above and in contact with the silver layerwhich is metallic and a SiO2 layer deposited by magnetron sputtering.

On the other hand, it is known, for example from WO2012/160145, todeposit SiO2 coatings by plasma enhanced chemical vapour deposition(“PECVD”), to increase the efficiency of SiO2 deposition compared toSiO2 by sputtering. But we found that simply replacing sputtered-SiO2 byPECVD-SiO2 in such type of coating stacks caused a lot of difficulties.In particular we could not reach at the same time a low haze value and agood resistance to abrasion (see our comparative examples 4 to 9hereunder).

The aim of the invention is therefore to seek to develop a new type ofcoating stack with solar control properties which is efficient in termsof optical and energetical properties, which maintains these propertiesafter a possible heat-treatment, which is chemically and mechanicallyresistant, which is aesthetically pleasant (neutral colour and low haze)and which is practical and efficient to manufacture.

In the present invention, the following conventions are used:

-   -   The luminous transmission (LT) is the percentage of incident        luminous flux, of Illuminant D65/2°, transmitted by the glazing.    -   The luminous reflection (LR) is the percentage of incident        luminous flux, of Illuminant D65/2°, reflected by the glazing.        It can be measured on coating side (LRc) or substrate side        (LRg).    -   The energetic transmission (ET) is the percentage of incident        energetic radiation transmitted by the glazing calculated        according to standard EN410.    -   The energetic reflection (ER) is the percentage of incident        energetic radiation reflected by the glazing calculated        according to standard EN410. It can be measured on coating side        (ERc) or substrate side (ERg).    -   The solar factor (SF or g) is the percentage of incident        energetic radiation which is partly directly transmitted by the        glazing and partly absorbed by it, then radiated in the        direction opposite to the energetical source in relation to the        glazing. It is herein calculated according to standard EN410.    -   U value and emissivity (c or E) are calculated according to        standards EN673 and ISO 10292.    -   CIELAB 1976 values (L*a*b*) are used to define colours. They are        measured with Illuminant D65/10°.    -   ΔE*=√{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)} represents the        tint variation during the heat treatment, i.e. the difference        between before and after heat treatment colours.    -   Sheet resistance (R² or Rs), expressed in ohms per square (Ω/□),        measures the electrical resistance of thin films.    -   When values are said to be “comprised between a and b”, they may        also be equal to a or b.    -   The positioning of the coating stack in a multiple glazing is        given in accordance with the standard successive numbering of        glazing faces, face 1 being outside of the building or the        vehicle, and face 4 (in a double-glazing) or face 6 (in a        triple-glazing) being inside.

According to one of its aspects, the present invention provides aglazing as defined by claim 1. Dependent claims define preferred and/oralternative aspects of the invention.

The invention provides a glazing having a transparent substrate coatedwith a stack of thin layers comprising n functional layer(s) reflectinginfrared radiation and n+1 dielectric layers, with n≥1, each functionallayer being surrounded by dielectric layers. It is characterised by thefact that at least one dielectric layer above a functional layercomprises a layer consisting essentially of silicon oxide and by thefact that the stack comprises a barrier layer based on zinc oxide aboveand in direct contact with any functional layer which has a siliconoxide layer in the dielectric layer directly above it.

For the sake of clarity, when using terms like below, above, lower,upper, first or last herein, it is always in the context of a sequenceof layers starting from the glass below, going upward, further away fromthe glass. Such sequences may comprise additional intermediate layers,in between the defined layers, except when a direct contact isspecified.

Such glazing according to the invention, thanks to the specificcombination of a silicon oxide layer and a zinc oxide based barrier hasproven to offer the following advantages (stack of thin layers depositedon ordinary clear soda-lime float glass of 4 mm thickness, incorporatedinto a double glazing with another ordinary clear soda-lime float glassof 4 mm thickness, with a space in between of 15 mm, filled with 90%argon, the coating stack being in position 2):

-   -   a high luminous transmission, together with a low emissivity to        limit heat losses (single functional layer configuration stack:        LT≥73%, ε≤0.074 or ε≤0.044, preferably ε≤0.024; double        functional layer configuration stack: LT>68%, ε≤0.038,        preferably ε≤0.025);    -   a solar factor adjustment: low SF, but not too low, allowing the        energetical part of the sun radiation to go through and take        advantage of free energy in winter (e.g. single functional layer        configuration stack: SF between 55% and 65%); or lower SF        allowing to reduce the risk of excessive overheating due to        sunshine (e.g. double functional layer configuration stack:        SF<41%);    -   an insulation ability allowing to achieve a U value U≤1.3        W/(m²K) or U≤1.2 W/(m²K), preferably U≤1.1 W/(m²K) or U≤1.0        W/(m²K);    -   a neutral colour in transmission or reflection, in single or in        multiple glazing, with preferred values in single glazing of:    -   in transmission: −6≤a*≤+5 −6≤b*≤+6    -   in reflection coating side: −6≤a*≤+6 −25≤b*≤10    -   in reflection substrate side: −5≤a*≤+3 −20≤b*≤+4    -   the possibility of being heat treated, the coating stack being        able to undergo high temperatures, or being used without any        heat treatment;    -   an aesthetical aspect without defect, with a very limited or        non-existing haze without or after heat treatment, and the        absence of unacceptable spots after heat treatment;    -   in some cases, the conservation of substantially unchanged        optical and energetical properties after heat treatment,        allowing the use of heat treated or non heat treated products        beside each other (“self-matchability”): no or few colour        modification in transmission and refection (ΔE*≤8, preferably        ≤5, more preferably ≤2) and/or no or few change in the luminous        and energetical transmission and reflection values (Δ=|(value        before heat treatment)−(value after heat treatment)|≤5,        preferably ≤3, more preferably ≤2), in single and/or multiple        glazing;    -   a sufficient chemical durability for a use without heat        treatment or for the time interval before any heat treatment, in        particular a result at the Cleveland test according to ISO        6270-1:1998 (exposure to humid vapours coming from a tank of        deionized water heated to 50° C.) giving no discolouration        visible at the naked eye after 1 day, preferably after 3 days;    -   a sufficient mechanical resistance, in particular resistance to        abrasion, tested for example with the Wet Brush test (as        explained hereinbelow), and giving a score of less than 3.

The inventors have indeed found that it was essential to have thiscombination of silicon oxide layer and zinc oxide based barrier to reacha compromise between high resistance to friction (scrubbing) and lowhaze.

The invention thus relates to a coating stack having n functionallayer(s) reflecting infrared radiation and n+1 dielectric layers, withn≥1, each functional layer being surrounded by dielectric layers.Low-emissivity coatings generally include a single functional layerreflecting infrared radiation, whilst coatings having low-emissivity andanti-solar properties generally include two or three functional layersreflecting infrared radiation. Preferably the functional layerreflecting infrared radiation is a silver-based layer, consisting ofsilver or silver doped with for example palladium or gold, in aproportion of at most 5 Wt. %, preferably around 1 Wt. %. Incorporationof a low quantity of dopant in the silver-based layer may improve thechemical durability of the coating stack. Advantageously the functionallayer has a thickness of at least 6 nm or at least 8 nm, preferably atleast 10 nm; its thickness is preferably at most 22 nm or at most 20 nm,preferably at most 18 nm, or at most 16 nm. Such ranges of thicknessallow to reach the sought low emissivity and/or anti-solar properties,whilst keeping the requested luminous transmission. In the case of acoating stack with two functional layers reflecting infrared radiation,it may be preferred that the thickness of the second functional layer,i.e. the one furthest away from the substrate, be slightly greater thanthe thickness of the first functional layer. As an example, the firstfunctional layer may have a thickness between 8 and 18 nm and the secondfunctional layer between 10 and 20 nm.

According to the invention, at least one dielectric layer above afunctional layer comprises a layer consisting essentially of siliconoxide. This means, for example, that in a single functional layerconfiguration stack, a silicon oxide layer is present in the second,upper dielectric layer, and in a double functional layer configurationstack, a silicon oxide layer is present either in the second or thirddielectric layer, or in each of the second and third dielectric layers.The layer consisting essentially of silicon oxide may include othermaterials, e.g. aluminium, as long as they do not affect the propertiesof the layer and of the coating stack. Generally such additionalmaterials are present in the layer in a quantity of at most 10 at. %,preferably at most 5 at. %. The silicon oxide may be fully or partiallyoxidised, in a range going from SiO to SiO₂.

Advantageously, the layer consisting essentially of silicon oxide isobtained by plasma enhanced chemical vapour deposition (PECVD). PECVD isan efficient method to deposit silicon oxide, offering high depositionrate and allowing high speed deposition. However, PECVD may induce thepresence of contaminants in the layer, like hydrogen- or carbon-basedcontaminants, which might possibly be at least partially oxidised.Preferably these should be as low as possible. It may be advantageousthat the layer consisting essentially of silicon oxide has an extinctioncoefficient at a wavelength of 632 nm below 1E-4, a refractive index ofat least 1.466 and a carbon content of at most 3 at. %. This may offerhigh thermal durability to the silicon oxide layer, and ensure that thecoating stack incorporating such layer withstand at best a future heattreatment.

Preferably the layer consisting essentially of silicon oxide has athickness of more than 10 nm. This minimum thickness may ensure that thesilicon oxide layer acts as a barrier against diffusion of oxygen intothe coating stack and helps for the thermal, mechanical and chemicalstability of the coating. Preferably the layer consisting essentially ofsilicon oxide has a thickness of at most 125 nm, to avoid too much haze.

The stack according to the invention comprises a barrier layer based onzinc oxide above and in direct contact with any functional layer whichhas a silicon oxide layer in the dielectric layer directly above it.This zinc oxide based barrier layer comprises Zn in a quantity of atleast 50 at. %, preferably at least 60 at. %, more preferably at least70 at. %, still more preferably at least 80 at. %, of the metallic partof the oxide. Preferably the barrier layer consists of zinc oxide,optionally doped with aluminium. More preferably, the barrier layer is alayer of pure ZnO (denoted iZnO) or a layer of zinc oxide doped withaluminium (denoted AZO), in a proportion of at most 10 Wt. %, preferablyaround 2 Wt. %. Such barrier has been found to be essential to offerhigh mechanical resistance and low haze.

In a preferred embodiment, the stack comprises zinc oxide based barrierlayers, preferably consisting of zinc oxide, optionally doped withaluminium, above and in direct contact with each functional layer. Thismay help further improve the overall stability of the coating in termsof resistance to heat treatment, mechanical and chemical resistance,whilst offering good visual aesthetics.

The zinc oxide based barrier layer(s) may have a thickness of at most 35nm or at most 30 nm, preferably at most 25 nm or at most 20 nm, morepreferably between 1 and 20 nm, between 2 and 18 nm or between 3 and 18nm.

In preferred embodiments of the invention the first dielectric layerstarting from the substrate (i.e. the lowest dielectric layer) comprisesa layer of an oxide in direct contact with the substrate. Advantageouslysaid layer of an oxide, which is in direct contact with the substrate,is a layer of an oxide of at least one material selected from Zn, Sn, Tiand Zr. Preferably it is a layer of mixed zinc-tin oxide in which theproportion zinc-tin is close to 50-50 Wt. %, for example respectively52-48 Wt. % (Zn₂SnO₄). A mixed zinc-tin oxide may be advantageous as itshows a good deposition rate, a good durability, and it has lesstendency to generate haze after heat treatment of the coating stack.

The layer of an oxide in direct contact with the substrate preferablyhas a thickness of at least 5 nm, 8 nm or 10 nm, more preferably atleast 15 nm, still more preferably at least 20 nm. Such values ofminimal thickness may allow, inter alia, to ensure the chemicaldurability of the product which is not heat treated, but also to ensurethe resistance of the product to a heat treatment.

Advantageously, each dielectric layer under a functional layer (i.e. thefirst dielectric layer in a single functional layer configuration stack;the first and second dielectric layers in a double functional layerconfiguration stack; etc.) comprises a layer based on zinc oxide,directly in contact with said functional layer. Such a layer issometimes called “seed layer” and helps for the growth of silver aboveit. Said layer based on zinc oxide may consist of zinc oxide oroptionally be doped with other metals, for example aluminium, in aproportion of generally at most 10 Wt. %, preferably around 2 Wt. %. Itpreferably has a thickness of at most 15 nm, preferably between 1.5 and10 nm, more preferably between 2 and 8 nm.

The dielectric layers may additionally comprise one or more other layersthan those described hereinabove, as long as the direct contactsdescribed as essential herein are respected: for example, one or morelayers of dielectric material consisting of metal oxide, nitride oroxynitride, preferably ZnO, TiO₂, SnO₂, Si₃N₄, ZrO₂, zinc-tin mixedoxide or titanium-zirconium mixed oxide. In the case of a zinc-tin mixedoxide, it can show a zinc-tin proportion of around 50-50 Wt. %, or azinc-tin proportion of around 90-10 Wt. %. The presence of a highrefractive index material may further help to increase the luminoustransmission of the glazing. It can be for example an oxide comprisingone element selected from Ti, Nb et Zr, preferably a titanium-zirconiummixed oxide, for example in a weight ratio Ti/Zr of around 65/35.

The dielectric layers of single, double and triple functional layerconfiguration stacks may show the following optical thicknesses,expressed in nm:

single functional double functional triple functional layer stack layerstack layer stack first, lowest, from 20 to 160, from 20 to 160, from 20to 160, dielectric layer (in preferably 30 to 130, preferably 30 to 130,preferably 30 to 130, contact with more preferably 35 or more preferably35 or more preferably 35 or substrate) 40 to 110 40 to 110 40 to 110second dielectric from 20 to 160, from 40 to 220, from 40 to 220, layerpreferably 30 to 130, preferably 60 to 200, preferably 60 to 200, morepreferably 40 to more preferably 90 or more preferably 90 or 110 110 to190 110 to 190 third dielectric — from 20 to 160, from 40 to 220, layerpreferably 30 to 130, preferably 60 to 200, more preferably 40 to morepreferably 90 or 110, still more 110 to 190 preferably 35 to 90 fourthdielectric — — from 20 to 160, layer preferably 30 to 130, morepreferably 35 or 40 to 110

In some embodiments, the last, uppermost dielectric layer comprises aprotective topcoat, which is the last layer of the stack. It preferablyconsists of an oxide or a substoichiometric oxide comprising at leastone element selected from Ti and Zr; preferably it consists of atitanium-zirconium mixed oxide, for example in a weight ratio Ti/Zr ofaround 65/35. Such a layer may improve the chemical and/or mechanicaldurability of the glazing. This protective topcoat advantageously has athickness of at least 2 nm, preferably at least 3 nm; preferably itsthickness is at most 20 nm, at most 15 nm or at most 12 nm, morepreferably at most 10 nm or at most 9 nm.

In some embodiments of the invention, the stack of thin layers comprisesat least, or consists of, starting from the substrate:

-   (i) a layer of zinc-tin mixed oxide, having a thickness between 27    and 45 nm,-   (ii) a layer of zinc oxide, optionally doped with aluminium, having    a thickness between 1 and 8 nm, in contact with layer (iii),-   (iii) a silver-based functional layer, having a thickness between 7    and 16 nm,-   (iv) a barrier layer of zinc oxide, optionally doped with aluminium,    having a thickness between 1 and 32 nm, preferably between 1 and 18    nm, more preferably between 1 and 5 nm, in contact with layer (iii),-   (v) a layer of zinc-tin mixed oxide or a layer based on zinc oxide,    having a thickness between 15 and 35 nm,-   (vi) a layer of silicon oxide, advantageously deposited by PECVD,    having a thickness between 20 and 50 nm, preferably between 20 and    30 nm, and-   (vii) optionally a layer of titanium-zirconium mixed oxide, having a    thickness between 2 and 10 nm.

In other embodiments of the invention, the stack of thin layerscomprises at least, or consists of, starting from the substrate:

-   (i) a layer of titanium oxide, having a thickness between 25 and 35    nm,-   (ii) a layer of zinc oxide, optionally doped with aluminium, having    a thickness between 1 and 8 nm, in contact with layer (iii),-   (iii) a silver-based functional layer, having a thickness between 10    and 16 nm,-   (iv) a barrier layer of zinc oxide, optionally doped with aluminium,    having a thickness between 1 and 18 nm, preferably between 1 and 5    nm, in contact with layer (iii),-   (v) a layer of titanium oxide, having a thickness between 5 and 35    nm,-   (vi) optionally a layer of zinc-tin mixed oxide,-   (vii) optionally a layer of silicon nitride, layer (vi), in the    absence of layer (vii), having a thickness of at most 35 nm, or    layer (vii), in the absence of layer (vi), having a thickness of at    most 35 nm, or layers (vi) and (vii) having together a thickness of    at most 35 nm,-   (viii) a layer of silicon oxide, advantageously deposited by PECVD,    having a thickness of at most 45 nm, with a total thickness for    layer (vi), if any, and layer (vii) of between 20 and 45 nm, and-   (ix) optionally a layer of titanium-zirconium mixed oxide, having a    thickness between 2 and 10 nm.

In further embodiments of the invention, the stack of thin layerscomprises at least, or consists of, starting from the substrate:

-   (i) a layer of zinc-tin mixed oxide, having a thickness between 27    and 45 nm,-   (ii) a layer of zinc oxide, optionally doped with aluminium, having    a thickness between 1 and 8 nm, in contact with layer (iii),-   (iii) a silver-based functional layer, having a thickness between 7    and 16 nm,-   (iv) a barrier layer of zinc oxide, optionally doped with aluminium,    having a thickness between 1 and 35 nm, preferably between 1 and 18    nm, in contact with layer (iii),-   (v) a layer of silicon oxide, advantageously deposited by PECVD,    having a thickness between 20 and 100 nm, preferably between 20 and    80 nm, and-   (vi) optionally a layer of titanium-zirconium mixed oxide, having a    thickness between 2 and 10 nm.

In still further embodiments of the invention, the stack of thin layerscomprises at least, or consists of, starting from the substrate:

-   (i) a layer of zinc-tin mixed oxide, having a thickness between 27    and 45 nm,-   (ii) a layer of zinc oxide, optionally doped with aluminium, having    a thickness between 1 and 8 nm, in contact with layer (iii),-   (iii) a silver-based functional layer, having a thickness between 7    and 16 nm,-   (iv) a barrier layer of zinc oxide, optionally doped with aluminium,    having a thickness between 1 and 18 nm, preferably between 1 and 8    nm, in contact with layer (iii),-   (v) optionally a layer of zinc-tin mixed oxide or a layer based on    zinc oxide, having a thickness between 5 and 20 nm,-   (vi) a layer of silicon oxide, advantageously deposited by PECVD,    having a thickness between 20 and 125 nm, preferably between 20 and    100 nm,-   (vii) a layer of zinc oxide, optionally doped with aluminium, having    a thickness between 1 and 8 nm, in contact with layer (viii),-   (viii) a silver-based functional layer, having a thickness between 7    and 16 nm,-   (ix) a barrier layer of zinc oxide, optionally doped with aluminium,    having a thickness between 1 and 18 nm, preferably between 1 and 8    nm, in contact with layer (viii),-   (x) a layer of zinc-tin mixed oxide or/and a layer based on zinc    oxide, having a thickness, if appropriate together, of between 10    and 70 nm, and-   (xi) optionally a layer of titanium-zirconium mixed oxide, having a    thickness between 2 and 10 nm.

Advantageously, to minimise or avoid haze due to recrystallisation whena thick SiO2 layer is used, such layer may be split into two layersseparated by another dielectric material like a layer of zinc-tin mixedoxide or a layer based on zinc oxide. In the preceding embodiment, thiscould give, for example, the following sequence: . . .(iv)-(v)-(vi)-(v)-(vi)-(vii) . . . .

In still other embodiments of the invention, the stack of thin layerscomprises at least, or consists of, starting from the substrate:

-   (i) a layer of zinc-tin mixed oxide, having a thickness between 27    and 45 nm,-   (ii) a layer of zinc oxide, optionally doped with aluminium, having    a thickness between 1 and 8 nm, in contact with layer (iii),-   (iii) a silver-based functional layer, having a thickness between 7    and 16 nm,-   (iv) a barrier layer of zinc oxide, optionally doped with aluminium,    having a thickness between 1 and 18 nm, preferably between 1 and 8    nm, in contact with layer (iii),-   (v) a layer of zinc-tin mixed oxide or/and a layer based on zinc    oxide, having a thickness, if appropriate together, of between 10    and 70 nm,-   (vi) a layer of zinc oxide, optionally doped with aluminium, having    a thickness between 1 and 8 nm, in contact with layer (vii),-   (vii) a silver-based functional layer, having a thickness between 7    and 16 nm,-   (viii) a barrier layer of zinc oxide, optionally doped with    aluminium, having a thickness between 1 and 18 nm, preferably    between 1 and 8 nm, in contact with layer (vii),-   (ix) optionally a layer of zinc-tin mixed oxide or a layer based on    zinc oxide, having a thickness between 5 and 20 nm,-   (x) a layer of silicon oxide, advantageously deposited by PECVD,    having a thickness between 10 and 125 nm, preferably between 20 and    100 nm, and-   (xi) optionally a layer of titanium-zirconium mixed oxide, having a    thickness between 2 and 10 nm.

Glazing panels according to the invention are preferably used inmultiple glazing, for example as double or triple glazing. They mayadvantageously show the following properties:

Double glazing (DG) 90% Ar, coating in single functional layerconfiguration Single glazing (SG) position 3, paired with stack 4 mmclear glass a clear glass of 4 mm LT before | after heat treatment ≥73%,≥75%, ≥85% ≥65%, ≥75%, ≥78% LRc before | after heat treatment ≤25%,≤18%, ≤12% — LRg before | after heat treatment ≤25%, ≤18%, ≤12% — ETbefore | after heat treatment ≥50%, ≥55%, ≥58%, ≥60% — ERc before |after heat treatment ≤40%, ≤35%, ≤33% — ERg before | after heattreatment ≤34%, ≤30%, ≤27% — ΔLT, ΔLRc, ΔLRg, ΔE*_(T), ΔE*_(Rc),ΔE*_(Rg) ≤5, ≤3, ≤2 ≤5, ≤3, ≤2 before | after heat treatment Rs before |after heat treatment between 2 and 7 Ω/□, — between 1.5 and 4 Ω/□ ΔRs²before/after heat treatment ≤3.0, ≤2.0, ≤1.5 — g before | after heattreatment — between 55% and 75%, preferably between 58% and 65% Δgbefore | after heat treatment — ≤5, ≤3, ≤2 Colour in transmission a*between −5 & 5  before | after heat treatment b* between −6 & +6 Colourin reflection coating side a* between −4 & +4 before | after heattreatment b*  between −18 & +2 Colour in reflection glass side a*between −4 & +4 before | after heat treatment b*  between −18 & +2Emissivity <0.060, <0.050, <0.045, <0.035

Double glazing (DG) 90% Ar, coating in double functional layerconfiguration Single glazing (SG) position 3, paired with stack 4 mmclear glass a clear glass of 4 mm LT before | after heat treatment —≥55, ≥60%, ≥65% LRc before | after heat treatment ≤25%, ≤20%, ≤15% — LRgbefore | after heat treatment ≤25%, ≤20%, ≤15% — ET before | after heattreatment <55%, <50%, <45% — ΔLT, ΔLRc, ΔLRg, ΔE*_(T), ΔE*_(Rc),ΔE*_(Rg) ≤5, ≤3, ≤2 — before | after heat treatment Rs before | afterheat treatment between 0.8 and 3.5 — Ω/□, between 1.3 and 3 Ω/□ g before| after heat treatment — ≤41% Δg before | after heat treatment — ≤5%,≤3%, ≤2% Selectivity ≥1.75 Colour in transmission a* between −5 and 5 before | after heat treatment b* between −6 and +6 Colour in reflectionglass side a* between −7 and +7, between −4 and +4 before | after heattreatment b* between −20 and +2, between −15 and −3 Emissivity <0.045,<0.035, <0.025

According to some embodiments of the invention, the coating stack is“self-matchable”. This means there is no or only few change in theoptical and/or energetical properties, when the coated substrateundergoes a heat treatment of the type tempering or bending. This hasfor advantage that non heat treated and heat treated products can beplaced next to each other for the same application, e.g. within abuilding facade. Previously, it was on the contrary necessary to developand manufacture in parallel two types of coating stacks, one fornon-tempered glass, the other for glass to be tempered or bent, which iscomplicated both in terms of research and development efforts and interms of logistics, inter alia.

According to another of its aspects, the present invention provides aprocess of coating a transparent substrate with a stack of thin layersas defined by claim 16. Dependent claims define preferred and/oralternative aspects of the invention.

The invention provides in this respect a process of coating atransparent substrate with a stack of thin layers comprising nfunctional layer(s) reflecting infrared radiation and n+1 dielectriclayers, with n≥1, each functional layer being surrounded by dielectriclayers. Such process comprises depositing a layer consisting essentiallyof silicon oxide by plasma enhanced chemical vapour deposition (PECVD)as part of at least one dielectric layer above a functional layer anddepositing a barrier layer based on zinc oxide above and in directcontact with any functional layer which has a silicon oxide layer in thedielectric directly above it.

Plasma enhanced chemical vapour deposition (PECVD) is a process commonlyused to deposit thin films from a gas state (vapour) to a solid state ona substrate. Chemical reactions are involved in the process, which occurafter creation of a plasma of the reacting gases. PECVD can be carriedout using any plasma: non-thermal plasmas (out of equilibrium) orthermal plasmas (in equilibrium). Non-thermal plasmas are generallypreferred. The active entities of the plasma, such as electrons, ions orradicals, can bring about the dissociation or the activation of thechemical precursors. In order to keep the plasma out of equilibrium, itis often necessary to operate at reduced pressure. The majority of theknown PECVD techniques thus use low-pressure plasmas. Preferablydeposition of the layer consisting essentially of silicon oxideaccording to the invention is made by low-pressure PECVD.

The plasma can be generated via sources employing known devices whichare commercially available. Mention may be made, as plasma sources, ofPBS (Plasma Beam Source) sources, PDP (Penning Discharge Plasma)sources, microwave sources and ICP (Inductively Coupled Plasma) sources.Within the PBS sources, mention may be made of hollow-cathode plasmasources (see, for example, WO2010/017185) and linear dual beam plasmasources (Dual Beam PBS™) originating in particular from GPi (GeneralPlasma Inc.). In comparison with magnetron sputtering, PECVD givesaccess to plasmas having lower temperatures, which makes possible thedeposition of many more different materials.

Preferably, deposition of the layer consisting essentially of siliconoxide is made by PECVD using a microwave source, a hollow cathode sourceor a dual beam plasma source. Deposition of the thin layers of the stackother than the layer consisting essentially of silicon oxide ispreferably made by magnetron sputtering. Advantageously, both processes,PECVD and magnetron sputtering, can be integrated on a same line ofproduction, the PECVD source being placed in a coat zone of themagnetron coater.

Precursors of silicon that can be used in the PECVD process according tothe invention are silanes, disilanes, siloxanes amongst which TMDSO(tetramethyldi¬siloxane) and HMDSO (hexamethyldisiloxane) are preferred,silazanes, silylamines amongst which TSA (trisilylamine) is preferred,silicon alkoxides amongst which TEOS (tetraethyl orthosilicate) ispreferred, and silanols. Silane, TMDSO, HMDSO and TSA are preferred.

Embodiments of the invention will now be further described, by way ofexample only, with reference to examples 1 to 10, along with comparativeexamples 1 to 15. All the thickness values of the examples andcomparative examples are given in nm. Except otherwise stated, thesilicon oxide layers have been deposited by PECVD. Some with a hollowcathode source, of the type described in WO2010/017185 in aconfiguration of 1 meter width, under the following conditions: 20 kWAC, TSA precursor flow around 95 sccm from a central feed, recordeddynamic deposition rate of 300 nm/m_(/min). Others with a microwavesource, under the following conditions: 3 kW, 120 sccm HMDSO precursor,1000 sccm 02, dynamic deposition rate of 60 nm/m_(/min).

In the following tables, the following abbreviations are used:

-   ZnSnOx zinc-tin mixed oxide-   ZSO5 zinc-tin mixed oxide with a zinc-tin proportion of around 52-48    Wt. %-   ZnO:Al aluminium doped zinc oxide, deposited from a metallic target    in oxygen atmosphere-   AZO aluminium doped zinc oxide, deposited from a ceramic target in    neutral atmosphere-   AlSiN aluminium-silicon mixed nitride-   ZnSnOx:Al aluminium doped zinc-tin mixed oxide-   TiOx substoichiometric oxide of titanium-   AlN aluminium nitride-   SiN silicon nitride

COMPARATIVE EXAMPLE 1

The following stack of thin layers, not in accordance with theinvention, has been deposited by magnetron sputtering on a glasssubstrate:

ZnO:Al ZnSnO_(x) ZnO Ag (2 Wt. %) ZnSnO_(x) glass 32 5 13.3 15 41

It corresponds to a coating stack according to the teaching ofEP1140721. It shows a sheet resistance, before and after heat treatment,respectively of 3.342Ω/□ et 3.80Ω/□. Under examination with the nakedeye, the heat-treated product shows inacceptable haze and spots.

Compared to example 9, this demonstrates the advantage of having asilicon oxide layer in the second dielectric layer to minimise or avoidhaze and spots after heat treatment.

COMPARATIVE EXAMPLES 2 AND 3

The following stacks of thin layers, not in accordance with theinvention, have been deposited by magnetron sputtering on a glasssubstrate:

c. ex. 2 AlSiN ZnSnO_(x):Al TiO_(x) ZnO:Al Ag ZnSnO_(x):Al ZnO AlNZnSnO_(x) glass 43 4 0.9 7.7 8 7.7 1.3 50 12 c. ex. 3 AlSiN ZnSnO_(x):AlTiO_(x) ZnO:Al Ag ZnSnO_(x):Al ZnO AlN ZnSnO_(x) SiN glass 43 4 0.9 7.78 7.7 1.3 50 12 20

Before any heat treatment, they undergo a Cleveland test to measuretheir chemical durability. Results are bad: already after one day,discolouration is visible with the naked eye, and after 3 days, it iseven more visible.

By comparison, examples according to the present invention do not showany discolouration visible with the naked eye, after one day, nor 3days, of Cleveland test. This demonstrates the advantage of havingpreferably and inter alia, a layer of an oxide in direct contact withthe substrate, for a better chemical durability of the non heat-treatedproduct.

COMPARATIVE EXAMPLES 4 TO 9

Single silver and double silver coating stacks according to Table I,including a metallic titanium barrier, have been deposited on a glasssubstrate of 3 mm thickness. Silicon oxide layers have been deposited byHollow Cathode PECVD, whilst other layers of the stack have beendeposited by magnetron sputtering. These are coating stacks not inaccordance with the invention.

The score of Brush test (AB Brush), haze (AB Haze), emissivity (AB E)and sheet resistance (AB Rs [Ω/□]) on heat-treated samples (heattreatment was carried out at 730° C. during 3 min 15 s for single silverstacks and 4 min for double silver stacks) are given in the table. Allcomparative examples show at least one value for these properties whichis unacceptable (underlined values in the table). By comparing c.ex.4and c.ex.5 or c.ex.6 and c.ex.7, it can be seen, for example, thatslightly increasing the thickness of the Ti barrier(s) improves theBrush score, but increases the haze.

This shows that it is not possible to reach at the same time a low hazevalue and a good resistance to abrasion, for coating stacksincorporating a PECVD silicon oxide layer and having a metallic barrierlayer.

Moreover, by comparing the colour in reflection of the coatingsaccording to c.ex.6-9 before and after heat treatment, we have notedthat such stacks are far from being self-matchable, with Delta E* ofmore than 10.

EXAMPLES 1 TO 5 AND COMPARATIVE EXAMPLES 10 AND 11

Single silver coating stacks according to Table II have been depositedon a glass substrate of 3 mm thickness. Silicon oxide layers in theexamples 1 to 5 according to the invention have been deposited by HollowCathode PECVD, whilst silicon oxide layers in the comparative examples10 and 11 not in accordance with the invention have been deposited bymagnetron sputtering. Other layers of the stacks have been deposited bymagnetron sputtering.

The score of Brush test (AB Brush), haze (AB Haze), emissivity (AB E)and sheet resistance (AB Rs [Ω/□]) on heat-treated samples (heattreatment was carried out at 730° C. during 3 min 15 s) are given in thetable, together with the Delta E* value in reflection on the coatingside.

All the examples according to the invention show good results in termsof resistance to abrasion, haze, emissivity and sheet resistance afterheat treatment. They furthermore show good results in terms ofself-matchability, with Delta E* of less than 5.0, preferably less than3.0, more preferably less than 2.0. On the contrary, samplesincorporating silicon oxide deposited by magnetron show at least onevalue for these properties which is unacceptable (underlined values inthe table).

In addition, the following properties were measured on example 1:

Single glazing (SG) LT before | after heat treatment 86.5% | 90.4% LRcbefore | after heat treatment 4.7% | 4.9% LRg before | after heattreatment 5.1% | 5.2% Rs before | after heat treatment 3.8 Ω/□ | 3.4 Ω/□

EXAMPLES 6 TO 8 AND COMPARATIVE EXAMPLES 12 AND 13

Double silver coating stacks according to Table III have been depositedon a glass substrate of 3 mm thickness. Silicon oxide layers in theexamples 6 to 8 according to the invention have been deposited by HollowCathode PECVD, whilst silicon oxide layers in the comparative examples12 and 13 not in accordance with the invention have been deposited bymagnetron sputtering. Other layers of the stacks have been deposited bymagnetron sputtering.

The score of Brush test (AB Brush), haze (AB Haze), emissivity (AB E)and sheet resistance (AB Rs [Ω/□]) on heat-treated samples (heattreatment was carried out at 730° C. during 4 min) are given in thetable.

All the examples according to the invention show good results in termsof resistance to abrasion, haze, emissivity and sheet resistance afterheat treatment. On the contrary, samples incorporating silicon oxidedeposited by magnetron show at least one value for these propertieswhich is unacceptable (underlined values in the table).

In addition, the following properties were measured on example 6:

Single glazing (SG) LT before | after heat treatment   73% | 69.6% LRcbefore | after heat treatment 6.8% | 6.4% LRg before | after heattreatment   9% | 11.1% Rs before | after heat treatment 2.8 Ω/□ | 2.4Ω/□

TABLE I ZSO5 ZnO:Al Ag Ti ZnO:Al SiO2 AB Brush AB Haze AB E AB Rs c. ex.4 31.9 5 8.5 2.2 27 25.9 5 0.99 0.14 4.7 c. ex. 5 42.6 6.7 8.5 2.4 29.731.4 2 1.13 0.13 5.2 ZSO5 ZnO:Al Ag Ti SiO2 ZnO:Al Ag Ti ZnO:Al SiO2 ABBrush AB Haze AB E AB Rs c. ex. 6 30 5 9 1.8 90 20 10 2 — 30 5 1.17 0.062.2 c. ex. 7 30 5 9 3 90 20 10 3 — 30 1 2.50 0.08 2.2 c. ex. 8 30 5 9 290 20 10 2.5 20 20 5 1.67 0.06 2.0 c. ex. 9 30 5 9 1.8 90 20 10 2.2 2020 5 0.49 0.06 2.1

TABLE II ZSO5 ZnO:Al Ag AZO ZnO:Al SiO2 AB Brush AB Haze AB E AB RsDelta E* ex. 1 32 5 8.5 15 17 26 1 0.11 0.08 3.4 1.4 ex. 2 32 5 8.5 1517 50 2 0.12 0.08 3.0 2.7 c. ex. 10 32 5 8.5 15 17 26   4.5 0.47 0.093.6 5.0 c. ex. 11 32 5 8.5 15 17 50   4.5 0.25 0.08 3.4 8.3 ZSO5 ZnO:AlAg AZO SiO2 AB Brush AB Haze AB E AB Rs Delta E* ex. 3 32 5 8.5 32 26 20.13 0.10 3.4 2.1 ex. 4 32 5 8.5 15 75   2.25 0.21 0.08 3.2 0.9 ex. 5 325 8.5 15 100 2 0.27 0.10 3.2 2.7

TABLE III ZSO5 ZnO:Al Ag AZO ZnO:Al SiO2 ZnO:Al Ag AZO ZnO:Al ZSO5 ABBrush AB Haze AB E AB Rs ex. 6 30 5 8.5 15 15 75 20 10 5 19 19 2.25 0.100.06 2.4 ex. 7 30 5 8.5 5 10 125 10 10 5 19 19 2   0.28 0.09 3.0 c. ex.12 30 5 8.5 15 15 75 20 10 5 19 19 4.5  1.09 0.03 3.1 c. ex. 13 30 5 8.57.5 — 125 20 10 5 19 19 4.75 0.57 0.07 3.5 ZSO5 ZnO:Al Ag AZO ZnO:AlSiO2 ZnO:Al Ag AZO ZnO:Al SiO2 AB Brush AB Haze AB E AB Rs ex. 8 30 58.5 15 15 75 20 10 15 17 50 2.25 0.37 0.06 2.2

EXAMPLE 9

The following stacks of thin layers, in accordance with the invention,has been deposited on a glass substrate of 4 mm thickness:

ZnO:Al ZSO5 (2 Wt. %) Ag AZO ZSO5 SiO2 glass 42.5 3 7.9 3 32 20

All the coatings have been deposited by magnetron sputtering, except thesilicon oxide layer which has been deposited by microwave PECVD.

The following properties were measured on example 9, before and after aheat treatment of 700° C. during 4 min. Moreover, under examination withthe naked eye, the heat-treated product has showed no inacceptable hazeor spots.

Single glazing (SG) LT before | after heat treatment 89.8% | 89.7% □before | after heat treatment 0.08 | 0.07 Colour in transmission L* 95.9| 95.8 before | after heat treatment a* −1.1 | −0.8 b* 0.8 | 0.6 Colourin reflection coating side L* 24.8 | 26.5 before | after heat treatmenta* −0.7 | −1.8 b* −0.4 | −0.1 Colour in reflection glass side L* 26.5 |27.4 before | after heat treatment a* −1.1 | −1.9 b* −2.9 | −3.1

COMPARATIVE EXAMPLE 14

A similar stack to example 9, but without SiO2 and thus not inaccordance with the invention, has been deposited on a glass substrateof 4 mm thickness, by magnetron sputtering:

ZnO:Al ZSO5 (2 Wt. %) Ag AZO ZSO5 glass 40 3 7.5 3 38.3

Performances to various tests (described hereunder) were comparedbetween example 9 and comparative example 14, showing the advantageouseffect of the PECVD SiO2 topcoat on coating hardness:

Before heat-treatment After heat-treatment C. Ex. 14 Ex. 9 C. Ex. 14 Ex.9 Washing test 1 1 1 — — Washing test 2 6 1 — — Taber test (dry) 6 2 2 1Taber test (wet) 6 3 3 1

EXAMPLE 10

The following stacks of thin layers, in accordance with the invention,has been deposited on a glass substrate of 4 mm thickness:

ZnO:Al TiO2 (2 Wt. %) Ag AZO TiO2 SiO2 glass 26.5 3 13.2 2 25 28

All the coatings have been deposited by magnetron sputtering, except thesilicon oxide layer which has been deposited by microwave PECVD.

COMPARATIVE EXAMPLE 15

A similar stack to example 10, but without SiO2 and thus not inaccordance with the invention, has been deposited on a glass substrateof 4 mm thickness, by magnetron sputtering:

ZnO:Al TiO2 (2 Wt. %) Ag AZO TiO2 ZSO5 glass 29.3 3 12.8 2 20 17

Performances to AWRT test (described hereunder) were compared betweenexample 10 and comparative example 15, showing again the advantageouseffect of the PECVD SiO2 topcoat on coating hardness:

C. Ex. 15 Ex. 10 AWRT (250) 7 8 AWRT (500) 5 9

Finally samples according to example 10 and comparative example 15 wereimmersed into solutions of various pH during 5 minutes then dried.Colour was measured before and after immersion and drying, and a colourchange □E* was calculated, showing the advantageous effect of the PECVDSiO2 topcoat on coating chemical resistance:

□E* □E* C. Ex. 15 Ex. 10 pH 2 2.1 0.1 pH 3.4 1.6 0.1 pH 5 0.4 0.1 pH 80.5 0.1 pH 12 0.7 0.1

Brush Test

The “Brush test” or “Wet Brush test” is used to evaluate the resistanceof the coating to erosion caused by scrubbing. Full details of this testare set out in ASTM Standard D 2486-00. Samples of coated glass weresubmitted to Test Method A. The samples were scrubbed wet (withdemineralized water), with a bristle brush, during 1000 cycles. Theirdegradation was then observed with the naked eye and compared. A scorewas assigned between 1 and 5, 1 meaning not degraded and 5 meaning verymuch degraded (entire coating removal).

Washing Test

The “Washing test” is used to evaluate the resistance of the coating toerosion caused by washing. A 40×50 cm square sample is introduced intoan industrial glass washing machine operating with demineralised water.While the sample is in contact with the rotating brushes, the forwardmovement is stopped for 60 s. In test 1, the brushes are switched off atthe same time while in test 2 they continue rotating. In both cases thewater keeps on running.

The degradation is observed with the naked eye and compared. A score isassigned between 1 and 6, 1 meaning not degraded and 6 meaning very muchdegraded (entire coating removal).

Taber Test

The “Taber test” is another test used to evaluate the resistance of thecoating to erosion caused by friction. A 10×10 cm square sample ismaintained on a steel plate rotating at a speed of 65 to 75 rpm. Each oftwo parallel weighted arms carries one specific abrasive small wheelrotating freely around a horizontal axis. The wheels are covered by afelt stripe (according to DIN 68861, supplied by Erichsen, attached tothe wheels). Each wheel lies on the sample to be tested under the weightapplied to each arm, which is a mass of 500 g. The samples may bescrubbed wet (with demineralized water) or dry. The combination of theabrasive wheels and the rotating supporting plate creates on the samplean abrasive crown, more or less pronounced according to the coatinghardness. A score of 1 to 6 is given to each sample having beingsubjected to the test after a total of 500 rotations, 1 being the bestscore showing a highly resistant coating and 6 being the lowest score.

AWRT

The “Automatic Web Rub Test” (AWRT) is again a test used to evaluate theresistance of the coating to erosion. A piston covered with a cottoncloth (reference: CODE 40700004 supplied by ADSOL) is put in contactwith the coating and oscillates over the surface. The piston carries aweight in order to have a force of 33N acting on a 17 mm diameterfinger. The abrasion of the cotton over the coated surface will damage(remove) the coating after a certain number of cycles. The test isrealised for 250 and 500 cycles, at separated distances over the sample.The sample is observed under an artificial sky to determine whetherdiscoloration and/or scratches can be seen on the sample. The AWRT scoreis given on a scale from 1 to 10, 10 being the best score, indicating ahighly resistant coating

What is claimed is:
 1. A process of coating a transparent substrate witha stack of layers comprising n functional layer(s) reflecting infraredradiation and n+1 dielectric layers, with n≥1, each functional layerbeing surrounded by dielectric layers, comprising: depositing a layerconsisting essentially of silicon oxide by plasma enhanced chemicalvapour deposition (PECVD) as part of at least one dielectric layer abovea functional layer and depositing a barrier layer based on zinc oxideabove and in direct contact with any functional layer which has asilicon oxide layer in the dielectric directly above it.
 2. The processaccording to claim 1, wherein the depositing of the layer consistingessentially of silicon oxide is made by low-pressure PECVD.
 3. Theprocess according to claim 1, wherein the depositing of the layerconsisting essentially of silicon oxide is made by PECVD using amicrowave source, a hollow cathode source or a dual beam plasma source.4. The process according to claim 1, further comprising: depositing oflayers of the stack other than the layer consisting essentially ofsilicon oxide by magnetron sputtering.
 5. The process according to claim1, wherein the layer consisting essentially of silicon oxide has athickness of more than 10 nm.
 6. The process according to claim 1,further comprising: depositing a barrier layer based on zinc oxide aboveand in direct contact with each functional layer.
 7. The processaccording to claim 1, wherein the barrier layer(s) consists (consist) ofzinc oxide, optionally doped with aluminium.
 8. The process according toclaim 1, wherein the barrier layer(s) has (have) a thickness of at most35 nm.
 9. The process according to claim 1, further comprising:depositing directly on the substrate a first dielectric layer comprisingan oxide.
 10. The process according to claim 9, wherein the dielectriclayer comprising an oxide which is deposited directly on the substrateis a layer of zinc-tin mixed oxide or a layer of titanium oxide.
 11. Theprocess according to claim 9, wherein the dielectric layer comprising anoxide which is deposited directly on the substrate has a thickness of atleast 10 nm.
 12. The process according to claim 1, wherein thefunctional layer(s) reflecting infrared radiation is a (are)silver-based layer(s).
 13. The process according to claim 1, whereineach dielectric layer under a functional layer comprises a layer basedon zinc oxide, directly in contact with said functional layer.
 14. Theprocess according to claim 13, wherein the layer based on zinc oxideunder a functional layer has a thickness of at most 15 nm.
 15. Theprocess according to claim 1, wherein at least one dielectric layerabove a functional layer comprises, between a barrier layer based onzinc oxide and a layer consisting essentially of silicon oxide, at leastone layer of a metal oxide different from the barrier layer and from thelayer consisting essentially of silicon oxide.
 16. The process accordingto claim 1, further comprising: depositing a last dielectric layerbetween a barrier layer based on zinc oxide and a layer consistingessentially of silicon oxide, the last dielectric layer comprising atleast one layer of zinc-tin mixed oxide or of titanium oxide.
 17. Theprocess according to claim 1, wherein the layer consisting essentiallyof silicon oxide has an extinction coefficient at a wavelength of 632 nmbelow 1E-4, a refractive index of at least 1.466 and a carbon content ofat most 3%.
 18. The process according to claim 1, wherein the barrierlayer(s) has (have) a thickness of between 1 and 25 nm.
 19. The processaccording to claim 13, wherein the layer based on zinc oxide has athickness of between 1 and 10 nm.
 20. The process according to claim 1,wherein the depositing of the layer consisting essentially of siliconoxide is made by PECVD using a hollow cathode source.